1. Technical Field
This application relates to a method for making by assembling a tool to and in a tool holder, and the tool and tool holder, and the assembled tool and tool holder.
2. Background Information
Rigid support of cutting tools held in machine tools such as lathes, milling machines, drilling machines, borers and the like is absolutely essential if good quality machining is to be carried out. Poorly supported tools will produce a poor surface finish, inadequate accuracy, unnecessary noise, low rates of metal removal, and lead to short tool life.
Machine tool spindles usually terminate in a tapered bore, so large end mills or other cutting tools having a tapered shank can be inserted directly into the spindle. Small and medium sized cutters are however inserted in a tool holder or in a clamping chuck which is rigidly, concentrically and removably assembled to the spindle end. To provide rigid support, the tool in turn must be firmly gripped by the tool holder, concentrically and yet removably so that the tool can be sharpened or replaced when worn.
With regard to firm gripping of the tool, an attractive method of execution is to insert the tool into its holder by shrink fit. This is achieved by either freezing the tool, or heating the tool holder, or both. The tool is then easily slid into its holder, and when both parts reach room temperature the tool is firmly gripped. This method has advantages in ensuring concentricity, and as the tool holder nose can be compactly designed, not requiring any moving parts such as chuck jaws. Tools held by shrink fit are known and can be seen in several U.S. patents, including U.S. Pat. Nos. 5,311,654, 5,979,912 and 6,234,729 to Cook, 6,260,858 to DeLucia, 6,315,506 to Mizoguchi, 6,511,077 to Voss et al., and 6,595,528 to Voss.
Tool rigidity can be further improved where a shoulder designed to abut the nose of the tool holder is provided on the cutting tool. Such shoulder can be produced by using a tool shank diameter smaller than the tool cutting diameter, or by providing a shoulder larger than the cutting tool diameter at the shank end adjacent to the cutting teeth.
To achieve an improvement in rigidity, said shoulder must be and remain, firmly in contact with the nose of the tool holder. It has however been found by experience that such contact is not assured where the cutting tool is held by a shrink fit. Whether or not the explanation for this offered by Cook in the foreword of U.S. Pat. No. 6,234,729 is correct or not, there is little doubt that the desired axial abutment between the tool shoulder and its holder is in practice unsatisfactory. In trying to deal with this problem, Voss et al. in U.S. Pat. No. 6,511,077 propose to add a chamfered ring to provide an abutting surface for the tool shoulder. The ring is however too thin to provide a satisfactory abutment surface, and its short length and tapered seat are not conducive to precise perpendicular alignment.
It should be noted that after the tool is gripped in a shrink fit, the application of axial pressure can not eliminate a small gap remaining between the abutment faces. Even assuming that a high axial force could overcome the shrink fit, a small gap could not be eliminated. This is because the metal will axially contract under such external force to bring the two abutment faces into contact. However, the moment the axial force is released, the metal springs back and the small gap appears once again. Thus there is a need for an methodology and system which provides an improved interface coupling between a tool and a tool holder.